Windows: official port -- UCRT static build, UTF-8 throughout, Low IL sandbox, ncurses TUI, installer; v0.6.0

Build
  * cross build switches to pkgsCross.ucrt64 (shell-win.nix); curl (Schannel),
    winpthreads and ncurses 6.6 are linked statically, so the release is
    cst-agent.exe + busybox.exe (busybox-w32 Unicode) with no extra DLLs
  * windres embeds a manifest with activeCodePage=UTF-8 and a version resource
  * ncurses 6.6 Windows console driver patches (mouse button state, A_DIM,
    wide-char declarations): scripts/patches/
  * scripts/bootstrap_msys2.sh builds the same release natively in MSYS2
    UCRT64; PR #1's MINGW64 notes now point there
  * vendor/tre-regex (musl's TRE) provides <regex.h> on MinGW

UTF-8
  * paths cross the system call boundary as UTF-16 (*W APIs); console code
    pages set to 65001 and restored on exit; files are read and written in
    binary mode
  * child output that is not valid UTF-8 is decoded from the console, OEM or
    ANSI system code page
  * read_file hides CR; edit_file, apply_patch and write_file keep CRLF line
    endings and a UTF-8 BOM

OS layer and processes
  * os_dir_* and cst_fnmatch replace the POSIX-only directory walks in
    subagent, plugins, skills, undo and fs_tools; realpath / path_under and
    symlink rejection work on Windows
  * every child goes through CreateProcessW with its own environment block
    inside a Job Object, so timeouts and Esc end the whole process tree

Sandbox (auto mode, "auto · lowil")
  * run_shell runs with a restricted Low integrity token; the workspace gets
    an inheritable Low label once, the sandbox TEMP is labeled Low, and the
    credentials file gets a no-read-up label
  * drive roots, the profile and system folders are never labeled
  * network commands still ask, since Low IL does not block the network;
    Access denied and MSYS2's 0xc0000142 offer a rerun outside the sandbox
  * /sandbox lists labeled folders, /sandbox reset-labels restores them

TUI
  * raster console fonts are switched to Consolas / NSimSun while running
  * the home logo falls back to text when the console font lacks U+2580
  * mouse drag copy goes to the Windows clipboard

Distribution
  * scripts/install_windows.ps1 installs a Gitea release into
    %LOCALAPPDATA%\Programs\cst-agent and adds it to the user PATH;
    cst-agent-update.cmd reruns it; scripts/release_windows.sh uploads the
    zip with the token taken from the environment
  * scripts/run_windows.bat is gone; docs/README-windows.md is rewritten

Tests
  * new test_lowil, test_win_utf8 and test_os_dir; tests made portable
    (cst_test_util.h)
  * scripts/win_test.sh and scripts/winvm/ run the suite on English and
    Chinese Windows Server VMs as Administrator, a standard user and a
    Chinese user name: 29/29 on all six

tests/test_sandbox.c

@@ -73,6 +73,43 @@ static void test_blocked(void) {
   const char *d = "curl: (7) Failed to connect to example.com port 443 after 9 "
                   "ms: Could not connect to server\n";
   CHECK(cst_sandbox_blocked(d, strlen(d), 7));
+  const char *e = "Access is denied.\r\n";
+  CHECK(cst_sandbox_blocked(e, strlen(e), 1));
+  const char *f = "拒绝访问。\r\n";
+  CHECK(cst_sandbox_blocked(f, strlen(f), 1));
+  const char *g = "sh: C:/msys64/usr/bin/ls.exe: A dynamic link library (DLL) "
+                  "initialization routine failed. Error 0xc0000142\n";
+  CHECK(cst_sandbox_blocked(g, strlen(g), 1));
+}
+
+static void test_network_rules(void) {
+  static const char *const NET[] = {
+      "curl -fsSL https://example.com",
+      "cd x && wget http://a/b",
+      "/usr/bin/ssh host ls",
+      "C:\\tools\\curl.exe -O x",
+      "git push origin main",
+      "git --no-pager fetch",
+      "npm install",
+      "python -m pip install requests",
+      "go get example.com/x",
+      "cargo install ripgrep",
+      "Invoke-WebRequest -Uri x",
+  };
+  static const char *const LOCAL[] = {
+      "ls -la", "git status", "git commit -m push", "npm run build",
+      "make -j8", "pip list", "echo curly", "cat curl.txt",
+  };
+  for (size_t i = 0; i < sizeof(NET) / sizeof(NET[0]); i++) {
+    if (!cst_shell_uses_network(NET[i]))
+      fprintf(stderr, "expected network: %s\n", NET[i]);
+    CHECK(cst_shell_uses_network(NET[i]));
+  }
+  for (size_t i = 0; i < sizeof(LOCAL) / sizeof(LOCAL[0]); i++) {
+    if (cst_shell_uses_network(LOCAL[i]))
+      fprintf(stderr, "expected local: %s\n", LOCAL[i]);
+    CHECK(!cst_shell_uses_network(LOCAL[i]));
+  }
 }
 
 #if !defined(_WIN32)
@@ -314,6 +351,7 @@ static void test_confined(int kind) {
 int main(void) {
   test_rules();
   test_blocked();
+  test_network_rules();
   int kind = cst_sandbox_probe();
   printf("test_sandbox: sandbox %s\n", cst_sandbox_name(kind));
 #if !defined(_WIN32)